Option: f90

This setting provides detailed control over the warnings about
supported extensions to the Fortran 77 Standard that were not adopted
as part of the Fortran 90 Standard. Note that ftnchek does not
support the full Fortran 90 language. However, it does support some
common extensions to Fortran 77 that were prevalent before Fortran 90
was defined. Some of these extensions became part of the Fortran 90
Standard, but others did not. The -f90 setting warns only
about the latter. That is, this flag covers things that are neither legal
Fortran 77 nor legal Fortran 90. Therefore, the warnings controlled
by this flag are basically a subset of the warnings controlled by
-f77. There are a few cases, described below, where the
circumstances in which the warning is given are slightly different for
the two flags.

The list
consists of keywords separated by commas or colons.
There are three special keywords: all to turn on all the
warnings about nonstandard extensions, none to turn them all
off, and help to print the list of all the keywords with a brief
explanation of each.
If list is omitted, -f90 is equivalent to
-f90=all, and -nof90 is equivalent to
-f90=none.

The following keywords have identical meanings for -f90 as for
-f77. The reader is referred to the explanations under -f77.

accept-type

double-complex

param-noparen

backslash

format-dollarsign

cray-pointer

byte

format-edit-descr

quad-constant

cpp

function-noparen

type-size

d-comment

name-dollarsign

variable-format

dec-tab

param-implicit-type

vms-io

The keywords which differ somewhat from the corresponding
-f77 keywords are as follows.

continuation:

The limit on the number of continuation lines for a statement in
fixed source form is the
same, namely 19, in Fortran 90 as in Fortran 77. For free
source form the limit is 39 continuation lines, and a line containing
a continuation mark cannot be otherwise empty or contain only a comment.

intrinsic:

This is the same as for -f77 except for the intrinsic
functions defined in MIL-STD 1753, which are all included in Fortran
90, and so are not warned about. (See -intrinsic for a list.)

io-keywords:

This is the same as for -f77 except that no warnings are given
for the I/O keywords that are standard in Fortran 90.

long-line:

Although the Fortran 90 Standard allows lines longer than 72
characters in free source form, this restriction still applies to fixed
source form. In free source form the line length limit is 132 characters,
and unlike fixed form, ftnchek does not allow this limit to
be increased.

mixed-expr:

This is the same as for -f77 except for expressions mixing
extended precision real with complex data types, which are permitted
in Fortran 90.

statement-order:

This is similar to the corresponding -f77 warning, but applies
the somewhat looser restrictions on statement order of the
Fortran 90 Standard. In particular, Fortran 90 allows DATA
statements and statement-function definitions to be intermixed with
specification statements.

typeless-constant:

In Fortran 90, binary, octal, and hexadecimal constants of the form
B'ddd', O'ddd', and Z'ddd', respectively, are
permitted. Here 'ddd' represents a string of digits.
ftnchek recognizes these forms, as well as a variant of the form
X'ddd' for a
hexadecimal constant, and other variants in which the base indicator
B, O, Z, or X
follows the digit string. These variants were not adopted in
Fortran 90, so only they are warned about when this flag is turned on.